Polychlorinated biphenyls, or "PCBs", were long used as dielectric fluids in electrical equipment because these materials have excellent heat stability, are nonflamable in nature, and have low volatility and good viscosity characteristics at normal operating temperatures.
In 1976, congress enacted the Toxic Substances Control Act (TSCA) as a response to public concern over hazardous waste. PCBs were the only substances named in the act. On May 31, 1979, the EPA published the PCB "Ban Rule" regulating fluids containing over 50 parts per million (ppm) PCBs. Since promulgating the "Ban Rule", the EPA has issued many additional regulations addressing PCB-related issues and defining various uses and restrictions on PCB fluids and equipment containing PCBs.
Because of these PCB concerns and the potential risk and liabilities associated with the use and removal of PCB fluids and equipment from service, facility owners must carefully evaluate the various options for disposing of PCBs and PCB contaminated equipment. While EPA regulations do permit the destruction of PCB-contaminated combustible fluids by incineration in an approved manner or disposal of PCB contaminated materials in an improved landfill, such procedures have not been particularly acceptable to the surrounding community and are costly.
Considering the case of liquid-filled power transformers, the majority in service today use either mineral oil or PCBs as their insulating fluid. While both fluids were used separately in their intended application, many mineral oil filled transformers were contaminated with PCBs during manufacturing or servicing. While the estimated number of contaminated units in service vary, there are at least 2.5 million transformers contaminated with more than 50 ppm of PCBs and considerable more units with more than 5 ppm of PCBs. Since many states are enforcing rules requiring clean up of PCB spills where contamination levels are as low as 5 to 10 ppm, the quantity of PCB contaminated oil still in use and which will be or is subject to regulation and disposal is vast.
As an alternative to incineration as a means for destroying PCBs, various processes have been proposed for chemically destroying PCBs. One of these processes involves the use of metallic sodium which, although effective, requires special handling, and trace amounts of water must be eliminated to minimize dangerous side reactions. Another effective approach to the chemical destruction or decomposition of PCBs which is considerably safer is to react the PCBs in transformer oils with a suitable glycol, such as polyethylene glycol (PEG) and a suitable alkali metal hydroxide, such as potassium hydroxide (KOH). Both PEG and KOH are non-proprietary chemical substances commonly used in industry and do not pose any unusal hazards. Complete reaction of the PCBs with the PEG and KOH reagents occurs quickly under relatively mild process conditions, producing decontaminated transformer oil and a non-PCB byproduct. The small quantities of byproducts produced are insoluble in transformer oil and thus are easily removed.
While sodium based processes destroy PCBs by sequentially stripping away chlorine atoms from the biphenyl molecule over time, the process utilizing the PEG and KOH reagents destroys PCBs by virtue of a simple chemical substitution of a glycol atom for a chlorine atom in the biphenyl system. While multiple substitutions of chlorine atoms may occur, only a single substitution is needed to render the PCB byproduct molecule insoluble in the transformer oil. This non-PCB byproduct can be easily removed from the oil by a simple separation process, such as decanting. The non-PCB byproducts can be incinerated, while the decontaminated oil may be used as a fuel in conventional heating equipment.
For a more detailed description of this PCB chemical decomposition process utilizing alkali metal hydroxides in combination with suitable glycols, reference may be had to the commonly assigned Brunell U.S. Pat. Nos. 4,353,793; 4,351,718; and 4,410,422, as well as the commonly assigned Mendiratta et al. U.S. Pat. No. 4,663,027. The disclosures of these patents are incorporated herein by reference.